Current email tracking systems operate by adding a tracking mark such as a tracking pixel to emails sent. This tracking pixel is a reference to an image inserted in the Hypertext Markup Language (HTML) code of the email message. In order to show the message, email clients supporting images (most do, nowadays) will request the image (via its URL) to the tracking service servers. These tracking service servers interpret such a request as a signal that the email message has been read.
When a sender uses an email user agent (i.e. a program that allows to receive and send e-mail messages) to send an email message to a recipient, an email tracking application inserts the tracking mark in the HTML code of the email message, then submits the email message to the sender email user agent for sending, and finally sends the message's metadata to the tracking service server(s) for later reference. The sender email user agent sends the email message to the email service's server, which saves a copy of the email message in a memory thereof (or Sent folder) and transmits the email message to the recipient. When the recipient later uses his own email user agent (recipient email user agent) to view the message, the recipient email user agent will request the tracking mark to the tracking service server(s), signaling that the email message has been read.
This method of operation is typical of individual email tracking systems such as Mailtrack.
The problem this prior solution is that if at any time the sender uses an email user agent, different from the previous sender email user agent that was used to send the email message (referred from now on as different sender email user agent), to access said memory and view the content of the email message, the different sender email user agent will also request the tracking mark from the tracking service server(s), also indicating a reading of the email message. This request by the different sender email user agent is generally indistinguishable from the request of the recipient email user agent.
In the extreme case, where the recipient user email agent and the different sender email user agent are the same brand and model (e.g. the Apple email client on the respective iPhones of the recipient and the sender), the two requests will have the exact same content, making it impossible to tell whether it was the sender or the recipient who read the email message.
Most tracking systems resolve this problem by assuming that all reads have been done by recipients, which easily confuses most users, making them loose confidence in the reliability of the system. This problem is common to all individual email tracking systems operating in the way described before.